1. Field of the Invention
The present invention relates generally to an inspection apparatus for inspecting the shape and so on of an object to be inspected, and is directed more particularly to an inspection apparatus which can accurately inspect an object steadily regardless of variations or fluctuations of the circumstance around the object and fluctuations in the function of the inspection apparatus itself.
2. Description of the Prior Art
In the prior art inspection apparatus of this kind, as shown in FIG. 1, for instance, a body which will be a standard i.e. becomes a reference body 1 for the following inspection, is located on inspection table T. While this reference body 1 is irradiated with the light from a light source 2, the reference body 1 is picked up by a television camera 3. The video signal from the television camera 3 is fed to a video signal processing device or circuit 4, which includes an A/D (analog to digital) converter 41 and a device or circuit 42 which extracts the features of the video signal to be processed. The output information or signal therefrom is fed to, for example, a computer 43 as a reference information signal for the following inspection which is memorized therein.
Then, an object to be inspected is located on the inspection table T at the same position as that at which the reference body 1 was located (therefore, the object is shown by the same reference numeral 1 as the reference body in FIG. 1). Then, the object 1 is picked up by the television camera 3 while being irradiated with the light from the light source 2. This video signal from the television camera 3 corresponding to the object 1 is similarly processed by the video signal processing circuit 4, and the output information signal therefrom is fed to the computer 43. This output information signal from circuit 4 corresponding to the object 1 is compared in the computer 43 with the reference information signal stored therein and then it is judged by the computer 43 whether the object is same as the reference body or not, or whether the object is good or not.
With the above prior art inspection apparatus, due to the fact that, during inspection of objects 1, the intensity or amount of the light irradiated on the objects from the light source 2 maybe different from that irradiated on the reference body 1 when it is picked up and/or due to the drift of the electric circuitry or circuit system including the television camera 3 and so on, the video signal from the television camera 3 which picks up the object 1 may become different from that corresponding to the reference body 1 even through the object is the same as the reference body. Thus, although the object is the same as the reference body, erroneous judgements that the former differs from the latter may occur.
In general, it is ordinary that the light source 2 is subjected to secular change or the circumferential light of the objects 1 is varied and hence the amount or intensity of the light irradiated on the object 1 is varied to an extent which can not be neglected through time lapse. Further, drift frequently occurs in the electric circuit system of the television camera 3 and so on. Therefore, in the prior art inspection apparatus the erroneous judgement set forth above inevitably appears frequently which is a fatal defect for such inspection apparatus.